Numerous known processes, and especially petrochemical processes such as catalytic cracking, or hydrotreating employ solid phase catalysts to facilitate the desired reaction. While most of the known catalysts significantly improve these processes, prolonged operation and relatively harsh process conditions frequently lead to deposition of carbon (typically in form of coke) on the catalyst, thereby at least partially inactivating the catalyst.
Consequently, numerous efforts have been made to regenerate carbon-contaminated catalysts, which is often achieved by combustion of the carbon on the solid phase with oxygen to produce carbon monoxide and carbon dioxide as a waste gas stream. Removal of carbon monoxide from the waste gas has become increasingly important due to increasingly stringent standards for atmospheric emission of waste gases, and there are various methods and configurations known in the art to reduce carbon monoxide emission from regenerator vessels.
For example, combustion of carbon to carbon dioxide may be performed in the same regenerator vessel at relatively high temperatures (e.g., above 1200° F.) to ensure combustion to carbon dioxide while substantially reducing the concentration of carbon monoxide in the effluent of the regenerator vessel (The combustion of carbon to carbon dioxide is a two-step reaction via the intermediate carbon monoxide). Exemplary configurations of such systems are described in U.S. Pat. Nos. 4,325,833 and 4,313,848 to Scott, in U.S. Pat. No. 4,051,069 to Bunn, Jr., et al., or in U.S. Pat. No. 4,991,521 to Green et al.
While relatively high temperatures generally reduce carbon monoxide emission, most, if not all regenerator vessels operating at such high temperatures will typically require expensive metals and other protective structures to withstand the thermal stress. Moreover, depending on the particular nature of the catalyst, sintering may occur at such temperatures. Still further, due to the relatively slow overall rate of conversion, regenerator vessels operating at high temperatures tend to be relatively large.
To circumvent at least some of the problems associated with high temperature, catalyst regeneration may be performed in separate vessels, wherein the carbon in the first vessel is incompletely combusted to a mixture of carbon monoxide and carbon dioxide, and wherein the mixture is then further combusted in a carbon monoxide boiler to carbon dioxide. Separate combustion of carbon monoxide in a carbon monoxide boiler to carbon dioxide typically provides an effluent gas with relatively low carbon monoxide concentration (e.g., less than 500 ppm). However, carbon monoxide boilers typically require significant quantities of energy for proper operation. Moreover, shutdown of the carbon monoxide boiler for maintenance or other reasons imposes a severe limitation on continuous operation of catalyst regeneration, and typically reduces regeneration capacity during shutdown at least 70%.
Thus, although many methods and configurations for catalyst regeneration are known in the art, all or almost all of them suffer from various disadvantages. Therefore, there is still a need to provide improved configurations and methods for catalyst regeneration.